During the War of the Titans the Hecatoncheires fought against the Titans—the first twelve of whom, like the Hecatoncheires, were the offspring of Gaia and Uranus—throwing rocks as big as mountains, one hundred at a time, and overwhelming them. After this, the Hecatoncheires became the guards of Tartarus. Briareos became the son-in-law of Poseidon, who gave him "Kymopoliea his daughter to wed".[11]

Hesiod's Theogony (624, 639, 714, 734–35) reports that the three Hecatoncheires became the guards of the gates of Tartarus.

In Virgil's Aeneid (10.566–67), in which Aeneas is likened to one of them (Briareos, known here as Aegaeon), they fought on the side of the Titans rather than the Olympians; in this, Virgil was following the lost Corinthian epic Titanomachy rather than the more familiar account in Hesiod.

In the first book of Homer's Iliad (c. 700 BC), Achilles asks his mother to appeal to Zeus on account of a previous interaction with Briareus, or Aegaeon.

Briareus is mentioned twice in Dante Alighieri's Divine Comedy (completed 1320); he is first found as a giant inhabiting the ninth circle of Hell[16] and then again as an example of pride, carved into the pavement of the first terrace of Purgatory.[17]

^A scholia on Apollonius Rhodius 1.1165c notes "Eumelos in the Titanomachy says that Aegaeon was the son of Earth and Sea, lived in the sea, and fought on the side of the Titans"; noted in M.L. West "'Eumelos': A Corinthian Epic Cycle?" The Journal of Hellenic Studies122 (2002, pp. 109–133) p 111.